movable-body navigation system such as a so-called car navigation system has been developed. In the movable-body navigation system, a current position of a movable body such as a motor vehicle is detected, the detected current position is displayed on a display screen together with a road map of surroundings, various guide information such as a destination and a route is displayed, and voice output is made.
In such an existing car navigation system, the current position of the movable body is checked as follows. That is, an autonomous-navigation controlling section performs tracing on a map previously stored as data in a storing means such as a CD-ROM (Compact Disc Read Only Memory) based on the speed pulses from a speed sensor and a direction obtained by earth magnetism from a geomagnetic sensor. In addition, a GPS signal transmitted from a GPS satellite is used. In the car navigation system in the early stage of the development in this field, there was an apparent malfunction (detection error) or the like in the past. That is, due to a measurement error or the like, an actual traveling position is significantly deviated from the trace position on the map. For example, when a vehicle is traveling along the coast actually, the traveling position of the vehicle detected by the car navigation system is indicated in the sea. However, for addressing such a significant position deviation, a technique of position correction (map matching) and the like have been developed. Therefore, in these days, the precision of detecting the traveling position of the vehicle is sufficient.
By superimposing information of the current position of the vehicle obtained as above on map information obtained from a large-volume data storing means such as a CD-ROM, an image showing the current position and the road map in a given range in the vicinity thereof can be displayed as a plane map-like two-dimensional image on a screen of an image display unit such as a liquid crystal display unit. In addition, it is possible to display so-called navigation information such as a vehicle position, a traveling direction, speed, map information, a course guide, the shortest route, and road information by being superimposed on the two-dimensional image map, or by being inserted in an appropriate position in the two-dimensional image map.
In some existing navigation display units, an image of information, for example, a traveling position and a traveling direction indicated by an icon of an arrow or the like, a recommended route (optimal route) from the current position to the destination is displayed by being superimposed on a two-dimensional image road planar map or on a road map that shows the surrounding landscape in a state of a three-dimensional CG. Further, in some existing navigation display units, traffic jam information or the like obtained by a VICS sensor or the like is displayed with a text label on the screen.
However, such an existing technique can only provide indirect navigation information using the plane (two dimensional) simplified map and the image expressed three dimensionally but abstractly and simply expressed by CG. Therefore, for a driver in the motor vehicle, there are problems, for example, as follows. That is, it is not possible to intuitively recognize a relation between the information such as the current position and the course guide and the road in the landscape actually seen through the windshield.
To solve the foregoing problems, for example, in Patent document 1, Patent document 2 and the like, a navigation system using a real picture in addition to the map information is proposed.
In the technique disclosed in Patent document 1, a current position and a traveling direction of a movable body are detected, and navigation information to be displayed according to the detected current position and the detected traveling direction is selected. An image of the navigation information read according to the current position of the vehicle is superimposed on a real picture captured by an image pickup device from a camera angle approximately similar to a landscape ahead of the vehicle in the traveling direction seen through the windshield of the vehicle, and the superimposed result is displayed on a screen or the like of a liquid crystal display panel. It is stated in Patent document 1 that a relation between the picture of the real road, the surrounding landscape thereof and the navigation information can be displayed easily recognizable visually. Further, in a general car navigation system, the navigation information is mainly picture information displayed on the picture display section. Therefore, there is a possibility that a driver gets distracted easily while driving.
Therefore, in Patent document 2, the following technique is proposed. That is, an image pickup device such as a CCD camera that captures a landscape ahead of a body for motor vehicle is provided, for example, in a position near the ceiling of the windshield of the vehicle or in the vicinity of the dashboard. A picture (image) of the landscape including a road ahead of the body for motor vehicle captured by the image pickup device is displayed by being inserted in a given position of the screen displaying map information as a sub-screen. According to such a technique, even when the driver of the vehicle views navigation information such as a map displayed on the screen of the image display unit while driving, the driver views the real picture of the landscape ahead of the vehicle displayed as the sub-image in the given position on the screen. It is stated in Patent document 2 that the driver can thereby comprehend a state in front of the vehicle without returning her/his attention to the landscape ahead of the vehicle.
Further, the following technique or the like has been proposed. In such a technique, setting is made so that, for example, when it is determined that an obstruction shown in the real picture of the sub-screen is large or when an object suddenly darts out from the side, the outer dimensions of the sub-screen (screen size) are enlarged. Thereby high-risk state in front of the vehicle is informed to the driver promptly and visually. In addition, such a high-risk state can be shown to the driver with high visibility. Consequently, safer driving can be secured.
Further, to determine the leading vehicle and operate automatic steering, it is necessary to more accurately comprehend the landscape including the road and the like ahead of the movable body as data. Therefore, for example, in Patent document 3, the following technique is proposed. In such a technique, a three-dimensional road shape is estimated by using image road information and map road information. In the technique disclosed in Patent document 3, the image road shape extracted from image data of the landscape ahead of the vehicle and map data around the vehicle are projected in one two-dimensional or three-dimensional logical space. Based on an overlapping state in the logical space of both of the projected road shapes, estimation is made for the road shape, a posture of the vehicle to the road surface, an absolute position of the vehicle and the like. In this technique, based on a picture captured by a monocular CCD camera, a sufficiently accurate road shape is estimated, and accurate determination of the leading vehicle and automatic steering are realized.    Patent document 1: Japanese Unexamined Patent Application Publication No. 10-132598    Patent document 2: Japanese Unexamined Patent Application Publication No. 11-304499    Patent document 3: Japanese Unexamined Patent Application Publication No. 2001-331787